One of the most important and essential tools in any metalworking shop is the drilling machine or drill press. Although the drilling machine is used primarily for drilling holes, it is often used for reaming, boring, tapping, counterboring, countersinking, and spotfacing.
Drilling machines typically operate on the same basic principle. The spindle turns the cutting tool as the cutting tool is advanced either by hand or automatically into a workpiece that is mounted on the table or held in a drill press vise. Successful operation of drilling machines generally requires a good knowledge of the machine, proper set-up of the work, correct speed and feed, and proper use of cutting fluids applied to the cutting tool and work.
Referring to FIG. 1, a known drill 99 is an end-cutting tool for producing holes. The drill 99 has one or more cutting edges 91, and flutes 92 to allow fluids to enter and chips to be ejected. The drill 99 is composed of a shank 93, a body 94, and a point 95 at the cutting end of the drill 99. The shank 93 is the part of the drill 99 that is held and driven (e.g. by a drill motor) and may be straight or tapered. The body 94 of the drill extends from the shank 93 to the point 95, and contains the flutes 92. During sharpening, it is the body 94 of the drill that is partially ground away. Flutes 92 are grooves that are cut or formed in the body 94 of the drill to allow fluids to reach the point and chips to reach the workpiece surface. Lands 96 are the remaining parts of the outside of the drill body after the flutes 92 are cut. In addition, the drill 99 has an outside diameter d, an axial length h along its axis a.
In use, cutters such as drills perform their function by rotating cutting edges 91 against a material in which a hole is desired. Imparting a torque on the shank 93 causes the rotation of the cutting edges 91. Often either because the length h of the drill may be inadequate to extend the cutting edges 91 to the desired depth of the hole, or because the shank 93 is broken or too short, it is desirable to braze onto the shank an extension.
Advantageously, shanks 93 are readily extended by brazing an extending shaft to the shank 93. In some instances, however, brazing a joint between the extending shaft (not shown) and the drill shank 93 may not produce a joint adequate to withstand the torque necessary to rotate the cutting edges 91 against the material. Failure of such a brazed joint is undesirable for a number of reasons. Therefore, methods and apparatus for torque-testing of brazed drill bits to test the brazed joint to determine its adequacy for suitable operation of the extended drill would have utility.